There are known resistive film type touch panel input devices having two dimensional touch input surfaces, that can detect the positions of points (touch points) on the touch input surfaces contacted by fingers or the like, as disclosed in Japanese Unexamined Patent Publication No. 2000-105645; Japanese Unexamined Patent Publication No. 2007-122522; and US Published Patent Application No. 2009/0322700.
This type of touch panel input device is basically constituted by: two resistive films which are arranged to face each other with a minute gap therebetween; an electrode pair (X electrode pair) formed by electrodes provided at the edges that face each other of one of the resistive films; an electrode pair (Y electrode pair) formed by electrodes provided at the edges of the other one of the resistive films that face each other and extend in directions perpendicular to the X electrode pair; means for applying voltages between the X electrode pair and between the Y electrode pair; and means for measuring the voltage which is divided at a touch point, when the resistive films are caused to contact each other by being touched.
In the configuration described above, the divided voltage which is measured between the X electrode pair corresponds to the resistance value of the resistive film from one of the electrodes to the touch point, that is, the distance between the electrode and the touch point. Therefore, the position of the touch point in the X direction can be detected by measuring this voltage. The same applies to the divided voltage which is measured between the Y electrode pair, and the position of the touch point in the Y direction is also detected. The two dimensional position of the touch point is detected in this manner.
Note that in touch panel input devices having the configuration described above, when two points are touched simultaneously, the voltage measured in the manner described above indicates an intermediate value between a value which is measured when one of the two points is touched and a value which is measured when the other of the two points is touched. Therefore, the substantial midpoint between the two points is detected. This point is disclosed in all of Japanese Unexamined Patent Publication No. 2000-105645; Japanese Unexamined Patent Publication No. 2007-122522; and US Published Patent Application No. 2009/0322700.
Meanwhile, US Published Patent Application No. 2009/0322700 in particular also discloses that it is possible to detect the distances between two touch points in touch panel input devices having the configuration described above, when two points are touched simultaneously. That is, when voltage is applied between one of the electrode pairs of the resistive films and two points are touched simultaneously, the resistance value between the electrodes is determined by the total resistance value of the resistive film, the two touch resistance values, and the resistance value between the two points within the other resistive film. Accordingly, the resistance value between the two points and the value of current that flows between the electrode pair will correspond to each other, and the resistance value between the two points is proportional to the distance between the two points. Therefore, the distance between the two points can be detected by measuring the current value that flows between the electrode pair.
US Published Patent Application No. 2009/0322700 also discloses that gestures, such as those in which the two touch points separate from each other, those in which the two touch points approach each other, and those in which the two tough points rotate with their approximate midpoint as the center of rotation, may be detected based on the above principle.
However, the touch panel input device disclosed in US Published Patent Application No. 2009/0322700 does not enable gestures more complex than those listed above to be detected. This point is common to conventional known resistive film type touch panel input devices.